The invention concerns an apparatus and a method for the production of porous or microporous tubing, through extrusion of a homogeneous mixture of a polymer and a liquid into a bath.
In German Offenlegungsschrift DE-OS No. 2 737 745 a series of microporous polymer structures and a method for their production are described. The structures display an excellent porous or microporous structure in the interior of the formed bodies, such as films or blocks, and possess valuable characteristics. Indications to work up such polymer-liquid systems into tubing are not however found in this reference. If one attempts in customary manner to produce tubing through extrusion, satisfactory results are not attained. There occur problems with regard to uniformity of wall thickness. Moreover, the desired microporous structures are not obtained. Also, irregularities in the surfaces can be noted. Finally, the tubings often tend to collapse.
In German Offenlegungsschrift De-OS No. 2 833 493 methods for the production of porous hollow filaments from polymer-liquid-combinations are described, such as those combinations disclosed in German Offenlegungsschrift DE-OS No. 2 737 734. The methods described in DE-OS No. 2 833, 493 do not however carry over to the production of tubing.